Impact of ligands structure on formation of hydrophilic colloids from their Gd(III) complexes with high magnetic relaxivity

Abstract

© 2018, Institute of Chemistry, Slovak Academy of Sciences. The present paper introduces specific structure of thiacalix[4]arenes derivatives adopting 1,3-alternate conformation with alkyl-carboxyl substituents as ligands for conversion of their complexes with Gd(III) ions into hydrophilic colloids with longitudinal (r1) and transverse relaxivities (r2) higher than that of Gd(III)-based commercial contrast agents (r1 = 20.53 and r2 = 23.46 mM−1 s−1 at 0.47 T). pH-dependent coordination of Gd(III) ions via carboxyl substituents of the thiacalix[4]arenes is the driving force for the complex formation, while the precipitation of the complexes is the basis for the colloids formation. Tert-butyl and butyl substituents of thiacalix[4]arenes were found to be of crucial impact on the complex precipitation. The specific inner- and outer-sphere ligand environment provided by the thiacalix[4]arene ligands was revealed as the optimal for high r1 and r2 values of the colloids. High relaxivities along with negligible cytotoxicity open up the possibility of their further use as positive contrast agents in magnetic resonance imaging (MRI).